Internal combustion engines typically force pressurized exhaust gases through some form of an exhaust system which pipes the exhaust gases out into the atmosphere. When engine exhaust gases are forced out into the atmosphere under high pressure (i.e., with high energy) through an opening, a high decibel sound or noise is generated as the exhaust gases are expelled. Exhaust systems have been developed with various forms of noise reduction devices (i.e., mufflers) in an effort to reduce the noise levels caused by the exiting exhaust gases. Such exhaust systems are designed so that the exhaust gases flow through one or more mufflers before they exit into the atmosphere.
In general, mufflers reduce the exhaust noise levels by restricting the flow of exhaust gases through the muffler, causing the gases to exit to atmosphere at slower rates (i.e., under less pressure). As the flow of exhaust gases is restricted, a back pressure builds up in the exhaust system. Unfortunately, as the back pressure increases, the power output (horse power) and overall performance of the engine typically suffers. Therefore, in order to maintain engine exhaust noise at tolerable levels, the engine's optimum performance level is usually sacrificed.
The performance and power output requirements for some uses of combustion engines, such as in street vehicles, are less than that required for other applications, such as in high performance race cars. With regard to exhaust noise levels, regulations governing conventional street driven vehicles typically mandate lower noise limits than the limits allowed in race car driving and other such applications, where engine performance and horse power are of primary importance.
Consequently, the muffler of a standard street vehicle is designed to reduce noise levels and allows higher exhaust back pressures to build up. In contrast, the muffler of a high performance racing engine, which requires higher performance and greater horse power than a standard street car, is designed to allow higher noise levels to be reached in order to reduce back pressures.
While comparatively high noise levels are considered less of a nuisance in applications like race car driving, there are still limits to the level of engine noise allowed during, for example, an IMSA grand prix auto race. Even mufflers designed to satisfy these more tolerant noise level requirements cause back pressures to develop which can significantly impact the performance of an engine and its horse power. Thus, regardless of how the internal combustion engine is used (e.g. in a street car, race car, lawn mower, etc.), there is a continuing need for a muffler capable of lowering exhaust noise levels without a significant detrimental affect on engine performance and power output.